1. Field of the Invention
The present invention relates to an image compensation system and methods for video appliances, such as a color television receiver, etc., which compensates automatically for hue, saturation, contrast, brightness, and white balance of an image, corresponding with the exterior environment of the appliance.
2. Description of the Prior Art
Conventional video appliances, especially a television receiver generally adopts a skin color compensation circuit and an automatic brightness control circuit, as an image signal processor.
The skin color compensation circuit analyzes a received image signal, and if the signal is judged as a human skin color, the circuit provides a prescribed color, i.e., a skin color.
In practice, users often control human skin color when adjusting the picture of a television receiver. Skin color plays a standard part in adjusting the color of the picture.
The skin color compensation circuit, however, cannot properly cope with the variety of skin colors, because it merely checks without regard to exterior lightings whether or not an image signal is a skin color.
And it works in the same manner on colors analogous to skin color.
Therefore, an error in color reproduction may arise, and accordingly there will be some limiting factors on natural color reproduction.
The automatic brightness control circuit controls the brightness of a picture by sensing exterior brightness.
The attached FIG. 1 shows a bock diagram of a television receiver adopting the automatic brightness control circuit.
The television receiver is, with reference to FIG. 1, composed of a tuner 1 for tuning to an aiming station in broadcasting signals received by an antenna; an intermediate-frequency (hereinafter an "IF") signal processor 2 for processing an IF signal transformed from the tuned signal; a detector 3 for detecting an image signal and an audio signal from the IF signal processor 2; an audio processor 4 for processing the audio signal detected from the detector 3; a speaker 5 for making audio sound from the processed audio signal; a key selector 6, such as a key matrix, a remote control or the like, for providing a user's key instruction; a microprocessor unit (hereinafter an "MPU") 7 for allowing the tuner 1 to select an aiming station according to a user's key instruction, and for adjusting brightness of a picture by controlling the following video processor 8, corresponding with exterior brightness detected by the following brightness detector 10; a video processor 8 for controlling the brightness of a picture under the control of the MPU 7; a picture tube 9 for displaying the image processed by the video processor 8; and a brightness detector 10 for detecting exterior brightness, which provides it to the MPU 7.
In operation, the MPU 7 controls the tuner 1 to select an aiming station according to the instruction from the key selector 6. The selected station signal is transformed into an IF signal at the IF signal processor 2. The IF signal is provided to the detector 3.
The detector 3 detects an image signal and an audio signal from the IF signal and provides the image signal to the video processor 8 and the audio signal to the audio processor 4.
The audio processor 4 performs amplification of the audio signal and various functions, such as stereo reproduction or multivoice processing, and provides the processed signal to the speaker 5.
The video processor 8 performs amplification of the image signal and processing a color signal and a luminance signal, and provides the processed signals to the picture tube 9.
The brightness detector 10 detects exterior brightness using a sensor, such as a photoconductive cell (CdS), and converts the detected signal into a digital signal by an analog-to-digital converter built in the brightness detector 10.
The digitized signal is provided to the MPU 7. The MPU 7 performs an appropriate operation by using original brightness data CD, exterior brightness data Cl, and reference data CO, e.g., CD=CD.times.Cl/CO, and provides the resulting value to the video processor 8.
The video processor 8 compensates for the brightness data CD in accordance with the exterior brightness data Cl, and thereby the brightness of the picture tube 9 can be adjusted.
In such an automatic brightness control circuit, however, it is difficult to perform sufficient natural color reproduction because the circuit processes brightness (or contrast) only.
In fact, it is necessary to control all the image reproduction factors, i.e., hue, saturation, contrast, brightness, and white balance, for complete natural color reproduction. Without collective control of these factors, it is difficult to accomplish natural color reproduction, and it is difficult to properly represent an image bearing natural colors.